1. Field of the Invention
The present invention relates to a switched mode power supply having an input for receiving an input signal voltage, a flyback converter circuit arrangement and an output for delivering a regulated output signal voltage.
2. Description of the Related Art
Switched mode power supplies find ready use as power regulators in view of characteristics, such as, a high efficiency, a relatively light weight, a relatively small dimension, and a relatively low power dissipation. However, a particular disadvantage that can limit the adoption of a switched mode power supplies relates to their noise performance, and in particular line voltage harmonic distortion.
As an example, U.S. Pat. No. 5,353,213 discloses a flyback converter which is arranged to generate an additional voltage for charging a capacitor which is arranged to supply the required energy for the converter in the regions of the zero crossings of the input line signal voltage.
The present invention seeks to provide a switched mode power supply exhibiting advantages over known such supplies and which, in particular, exhibits, an improved line voltage harmonic distortion performance.
According to the present invention, there is provided a switched mode power supply of the type defined above, characterized in that the switched mode power supply includes a boost converter arranged to be operatively combined with the said flyback converter.
The advantageous combination of the boost and flyback functions within such a converter serves to improve the noise performance of the converter and can, in particular, lead to advantages of line voltage harmonic reduction.
The feature of the switched mode power supply as described above and including a diode in series with a boost inductor at the boost converter and a further diode in series with a flyback inductor of the flyback converter, is advantageous in separating current paths within the converter so as to prevent undesired reverse current through the flyback inductor.
The feature of the switched mode power supply as described above and including a boost inductor and a flyback inductor combined in a single inductor in series with the input, is advantageous in providing for a simplified arrangement in which the power supply can switch between boost and flyback modes.
The features of the switched mode power supply described above, wherein said combined inductor comprises a tapped inductor having a tap derived from the output of the converter, and wherein the combined inductor comprises a tapped inductor having a tap derived from the line voltage input, are advantageous in providing means for readily controlling the switching between boost and flyback modes.
The feature of the switched mode power supply as described above, which further includes an additional boost inductor connected in series with the said first boost inductor, and which further includes an additional inductor in the form of a flyback inductor connected between the input and the output, are advantageous in controlling the switch-over point between the two modes of operation.